Such a coin does not exist.
The Royal Mint produced no 1704 Crown coins.
A silver pattern crown coin is a British coin that was produced between 1707 and 1965. This coin is made of silver and has a profile picture of Queen Victoria on it.
It's impossible to say for certain, as the question omits the coin's denomination. A silver coin for that year could be a threepence, sixpence, shilling, florin, or half crown.
The value of a silver coin is always changing because the value of silver is always changing. See the related link below for a silver coin value calculator. This does not give the actual value of the coin but it does give the value of the metal used to make the coin. This is know as the melt value.
It depends on the condition, but if circulated the coin sells for scrap silver (it is 50% silver) about $8 at the time of writing.
Metal value depends on the purity of the silver and the weight of the coin. Numismatic value depends on the condition of the coin.
All Peace dollars have this. It's just a normal part of the design and adds nothing to the value.
A Silver Eagle Bullion coin is 99.9% pure silver and weighs 1 oz per coin. The stamped value of the coin is U.S$1 however the intrinsic value of the coin is the value of the silver within that coin. If the the spot price of silver was $30oz at the time of checking, then the value of that coin would be worth at least $30 or more.
The silver content of the 1981 British Royal Wedding commemorative general circulation crown is zero. It is a cupro-nickel coin. No British general circulation coin has had any silver content since 1946. The 1981 silver Proof FDC Crown coin which was sold in a case, has a 92.5% silver content.
The coin could be anything from a Penny to a Crown. I expect it is difficult to describe because the inscriptions are in Latin and barely legible. Take your coin to a reputable coin dealer for a positive identification and valuation.
1959 Bermuda Crown: On a purely Scrap silver basis at today's silver price (27/03/2013) its £15.89 (28.28g of .925 Ag).The 1964 Bermuda Crown is £6.87 (22.62g of 50% silver).Obviously collectors may pay much more for coins in good condition.
The value of an uncirculated 1999 Silver American Eagle Littleton coin fluctuates based on the market for silver. However, a coin can be expected to have a value of about $40.
This coin is most likely worth the silver value.